Israel should have better prepared for Hamas's use of tunnels in the 2014 Gaza war, a senior army official said Sunday, ahead of the release of a key report on the conflict.

Speaking to AFP on condition of anonymity, the official said Israel's military has sought to learn lessons from the 2014 war, including by better preparing troops to deal with tunnel warfare.

The official's comments come ahead of a report by Israel's state comptroller on the conflict expected to be released before the end of the year.

A draft of the report reportedly found that "the security establishment did not have a comprehensive plan for dealing with Hamas's offensive tunnels".

The army has conducted its own internal review of the conflict, which also found that the military was unprepared for the tunnel threat.

The official, who has read the internal review of some 182 pages completed several months ago, said: "I think that we could come to this war... better than we came to it."

"I think the (military) did not do a good enough job to close a gap between the problem and the solution," he said.

Special engineering units have since been bolstered, the official said. Efforts have also been made to increase collaboration between units.

Israel is also reportedly building an underground wall around Gaza to block tunnels.

"We tried to learn and to teach ourselves what we need to do," the official said.

During the war, Israel's military found 32 tunnels, including 14 that extended from the Gaza Strip into Israel, according to a UN inquiry into the conflict.

Militants in Gaza, run by Islamist movement Hamas, used the tunnels during combat, including to carry out cross-border attacks.

The new threat of attack tunnels led to deep concern in Israeli communities bordering Gaza.

But despite criticism over Israel's handling of the tunnel threat, the Gaza Strip suffered an overwhelmingly higher number of victims and amount of damage in the 2014 war.

The 50-day conflict killed 2,251 Palestinians and left 100,000 homeless.

On the Israeli side, 73 people were killed, most of them soldiers.

The UN report said both Israel and Palestinian militants may have committed war crimes, decrying "unprecedented" devastation and human suffering.

The upcoming Israeli comptroller's report on the conflict may pressure Prime Minister Benjamin Netanyahu, who has faced criticism from political opponents over the tunnels.

Netanyahu has reportedly asked the comptroller for another hearing to defend his government's handling of the issue by explaining that the cabinet had repeatedly discussed it in-depth.